This invention relates to gate valves and, more particularly, to inserts used in gates or seats of gate valves for cutting wireline or tubing run through the valve flow path.
Gate valves are used to shut off or open a pressurized fluid flow path. Gate valves are typically comprised of a valve body having a valve chamber therein with an inlet port and outlet port, and a linearly moveable gate or slab having a through hole which when aligned with the inlet and outlet ports forms a flow path. The gate is moved linearly to open and close the flow path. Usually, one or more ring-shaped seat components are positioned on either side of the gate and around the flow path to form seals between the gate and the valve body.
Gate valves are commonly used in various oil or gas well operations. During operations which require the use of a wireline or tubing tool run through the well, there is the need for a mechanism that is capable of shearing the wireline or tubing under certain circumstances. To accomplish this, known gate valves have been designed to have shearing surfaces on the inner circumferential edges of either the gate or seat flow passage so that when the gate is moved from an opened position to a closed position, the wireline is sheared by these shearing surfaces. As a result of such shearing, the gate and seat surfaces can become damaged and ineffective as sealing surfaces. Replacement of such damaged parts is often expensive and disruptive to well operations.
Known valves designed to address the aforementioned problems have included the use of hardened inserts in either the gate or seats, or both. Even with the use of hardened inserts, some damage from wireline shearing still occurs and adversely affects the sealing capability of the components. Further drawbacks to such designs include the need to press-fit or otherwise hold gate inserts in place to prevent them from sliding out of place when the gate is in the closed position.
Another known design that attempts to solve the aforementioned problems includes the use of high strength, high hardness hardfacings on gates and seats for withstanding the high stress concentrations that occur during wireline cutting. Such hardfacings are usually expensive and often do not prevent deformation at the location of the cut and are subject to flaking or scratching, often resulting in leakage. When this occurs, replacement of the gate and seats is necessary and expensive.
There is a need, therefore, for a gate valve design that is capable of cutting a wireline or tubing, that is capable of maintaining a seal after cutting, and that is economical and practical.